Station

ABSTRACT

With the object of eliminating congestion that has occurred in a station which can not prevent or eliminate the occurrence of congestion autonomously, the SMPP response time in output interfaces  21   h - 21   k  of a first PPG  21  are measured and when the time mta, which is m-times of the SMPP response time ta in the normal state, is exceeded, congestion is assumed to occur in an interconnected station of the first PPG  21  and the response to push transfer request in an input interface  21   a  is delayed. Further, changes in the filling ratio in a buffer memory  21   b  are monitored and when the filling ratio exceeds h %, a decision is made that congestion has occurred in the first PPG  21  and the response to the push transfer request in the input interface  21   a  is delayed.

This application is the U.S. National Phase under 35 U.S.C. §371 ofInternational Application PCT/JP2004/002756, filed on Mar. 4, 2004,which claims priority of Japanese Patent Application No. 2003-071391,which was filed on Mar. 17, 2003. The International Application waspublished under PCT Article 21(2) in a language other than English.

TECHNICAL FIELD

The present invention relates to congestion control of a station forreceiving a message from an interconnected station on the input side andtransmitting the message information relating to the received message tothe interconnected station on the output side.

BACKGROUND ART

Recently developed cellular telephone systems can receive and transmitmultimedia messages including static images, dynamic images, and music.Such multimedia messages can be transmitted and received via internet bycellular telephones adapted to multimedia messages and can be exchangedbetween the cellular telephones adapted to multimedia messages.

An example of the configuration of the multimedia message allocationsystem is shown in FIG. 5.

Referring to FIG. 5, a MMS (Multimedia Messaging Service) 1 forms anucleus of a multimedia messaging service and controls storage,initiation of reception notification, and transfer of the receivedmultimedia messages. The MMS 1 has a mailbox for each subscriber andholds multimedia messages. A PPG (Push Proxy Gateway) 2 is a device forconducting push transfer by which message information of multimediamessages from the MMS 1 or the like is transferred by initiating thenetwork to the portable terminal 4 of a customer. A SMSC (Short MessageService Center) 3 conducts transmission and reception of short messagesto and from the portable terminal 4. The portable terminal 4 is acellular telephone adapted to multimedia messages. A WAP gateway(Wireless Application Protocol Gateway) 5 is a device forinterconnecting the internet connection from the portable terminal 4.

The processing flow during allocation of multimedia messages will beexplained below with reference to FIG. 5.

If the MMS 1 receives a multimedia message (MM-message), the MM-messageis stored in the mailbox of the subscriber, which is the customer in themailbox 1 a, a reception notification (Notification) to the customer isproduced, and transfer thereof is initiated. As a result, the MMS 1requests a push transfer of reception notification to the PPG 2. The PPG2 that received this request provides a session establishment request tothe SMSC 3 so as to initiate the network. The SMSC 3 that received thisrequest transfers to the portable terminal 4 a message that requests toestablish a session to the PPG 2. In this case, the SMSC 3 sends therequest to the portable terminal 4 as a short message.

The portable terminal 4 that received the request to establish a sessionto the PPG 2 establishes a session with respect to the PPG 2. As aresult, a state of possible communication is established between the PPG2 and portable terminal 4, and the PPG 2 sends a reception notificationfrom the MMS 1 to the portable terminal 4. The portable terminal 4 thatreceived the reception notification connects to the WAP gateway 5 andtransfers to the WAP gateway 5 the notification response (NotifyResp)that came from the portable terminal 4 to the MMS 1. The WAP gateway 5that receives the notification response sends the transferrednotification response to the MMS 1.

The portable terminal 4 then transfers to the WAP gateway 5 a HTTPrequest (HTTP GET) to acquire a multimedia message from the MMS 1 with aHTTP (Hypertext Transfer Protocol) which is a simple protocol composedof a request and a response corresponding thereto. The WAP gateway 5received it sends the transferred HTTP request (HTTP GET) to the MMS 1.The MMS 1 receives the HTTP request (HTTP GET) 1, reads the multimediamessage stored in the mailbox of the portable terminal and sends it viathe WAP gateway 5 to the portable terminal 4. As a result, the portableterminal 4 can receive the multimedia message for which the notificationhas been received.

In the PPG 2, the communication with the SMSC 3 is conducted with thecommunication protocol called SMPP (Short Message Peer-to-Peer), butflow control in the SMPP is not clearly defined and this protocol isconsidered to be unable to prevent or eliminate the appearance ofcongestion autonomously as a processing system. The resultant problem isthat there is a risk of processing being interrupted or terminated inthe SMSC 3 or PPG 2 when congestion has occurred in the SMSC 3 or PPG 2.Flow control support was also considered, but in order to produce theSMSC or PPG supporting the flow control, all the existing devices ofthose types had to be replaced which was unrealistic from the standpointof cost.

Accordingly, it is an object of the present invention to provide astation such that even if congestion occurs in a station in whichcongestion cannot be prevented from occurring or eliminatedautonomously, the occurred congestion can be eliminated withoutadditional modifications.

DISCLOSURE OF THE INVENTION

In order to attain the above-described object, the present inventionprovides a station for receiving a message from an interconnectedstation on the input side and transmitting the message informationrelating to the received message to the interconnected station on theoutput side, this station comprising congestion control means composedof congestion detection means for detecting the occurrence of congestionin the interconnected station on the output side and response means forresponding by delaying for the prescribed time the response to therequest to receive and accept the message from the interconnectedstation on the input side when the occurrence of congestion has beendetected with the congestion detection means.

Further, in the station in accordance with the present invention, theprescribed delay time may be set to a time obtained by dividing theaverage response time from the interconnected station on the output sideby a session number in the interconnected station on the output sidethat is multiplied by a margin ratio.

Further, in the station in accordance with the present invention, thecongestion control means may have switching means for switching themessage information of the session in which the congestion has occurredto another session when the occurrence of congestion has been detectedin the congestion detection means.

Furthermore, in the station in accordance with the present invention,when there are a plurality of interconnected stations on the output sideand the congestion has occurred or a closed state has been assumed inall the sessions to specific interconnected stations on the output side,the switching means may distribute and send the message information toother interconnected stations on the output side.

Further, in the station in accordance with the present invention,congestion detection means may detect that congestion has occurred inthe interconnected station on the output side when an error indicatingcongestion has been returned from the interconnected station on theoutput side in response to a request to transfer the message informationto the interconnected station on the output side.

Furthermore, in the station in accordance with the present invention,the congestion detection means may detect that congestion has occurredin the interconnected station on the output side from a parameterrepresenting a congested state in the response from the interconnectedstation on the output side to a request to transfer the messageinformation to the interconnected station on the output side, thisparameter being contained in the response.

Further, in the station in accordance with the present invention, thecongestion detection means may detect that congestion has occurred inthe interconnected station on the output side when the average responsetime in a plurality of the latest responses has reached m times (wherem>1) of the average response time in the normal state, in the responsefrom the interconnected station on the output side to a request totransfer the message information to the interconnected station on theoutput side.

Further, in the station in accordance with the present invention, thecongestion detection means may have issuance means for issuing a circuitstate verification request with a prescribed period with respect to asession in the interconnected station on the output side that has beendetected to be in a congested state in the congestion control means, andthe congestion detection means may detect that a congested state in thesession has been eliminated when the average response time in aplurality of the latest responses to the issued requests from theissuance means became equal to or less than the average response time inthe normal state.

In order to attain the above-described object, the present inventionprovides another station for receiving a message from an interconnectedstation on the input side and transmitting the message informationrelating to the received message to the interconnected station on theoutput side, the another station comprising congestion control meanscomposed of congestion detection means which detects the occurrence ofcongestion in the own station when the filling ratio in a buffer memorythat stores the messages or received requests that have not beencompletely processed exceeds the prescribed filling ratio, and responsemeans for responding by delaying for the prescribed time the response tothe request to receive and accept the message from the interconnectedstation on the input side when the occurrence of congestion in the ownstation has been detected in the congestion detection means.

Further, in the other station in accordance with the present invention,the prescribed delay time may be a time obtained by dividing the averageresponse time from the interconnected station on the output side by asession number in the interconnected station on the output side that ismultiplied by a margin ratio.

Furthermore, in the other station in accordance with the presentinvention, the congestion control means may allow for the detection ofcongestion occurrence in the interconnected station on the output sideand may have switching means for switching the message information ofthe session in which the congestion has occurred to another session whenthe occurrence of congestion in the interconnected station on the outputside has been detected in the congestion detection means.

Further, in the other station in accordance with the present invention,when there are a plurality of interconnected stations on the output sideand the congestion has occurred or a closed state has been assumed inall the sessions to specific interconnected stations on the output side,the switching means may distribute and send the message information toother interconnected stations on the output side.

Furthermore, in the other station in accordance with the presentinvention, the congestion detection means may detect that congestion hasoccurred in the interconnected station on the output side when an errorindicating congestion has been returned from the interconnected stationon the output side in response to a request to transfer the messageinformation to the interconnected station on the output side.

Furthermore, in the other station in accordance with the presentinvention, the congestion detection means may detect that congestion hasoccurred in the interconnected station on the output side from aparameter representing a congested state in the response from theinterconnected station on the output side to a request to transfer themessage information to the interconnected station on the output side,this parameter being contained in the response.

Furthermore, in the other station in accordance with the presentinvention, the congestion detection means may detect that congestion hasoccurred in the interconnected station on the output side when theaverage response time in a plurality of the latest responses has reachedm times (where m>1) of the average response time in the normal state, inthe response from the interconnected station on the output side to arequest to transfer the message information to the interconnectedstation on the output side.

Furthermore, in the other station in accordance with the presentinvention, the congestion detection means may have issuance means forissuing a circuit state verification request with a prescribed periodwith respect to a session in the interconnected station on the outputside that has been detected to be in a congested state by the congestioncontrol means, and the congestion detection means may detect that acongested state in a session has been eliminated when the averageresponse time in a plurality of the latest responses to the issuedrequests from the issuance means became equal to or less than theaverage response time in the normal state.

With the above-described present invention, when congestion occurs inthe own station or an interconnected station on the output side, theresponse to a request to receive and accept a message from theinterconnected station on the input side is delayed for the prescribedtime and the throughput on the input side is reduced. As a result, thedegree of retention on the output side can be gradually reduced and,therefore, the congestion of the own station or the interconnectedstation on the output side can be eliminated.

Furthermore, when congestion occurs in the interconnected station on theoutput side, message information of the session where the congestion hasoccurred is switched to another session and distributed to otherinterconnected stations on the output side. As a result, the congestionin the interconnected station on the output side can be eliminated evenfaster. The occurrence of congestion in the interconnected station onthe output side can be detected from the average response time orparameters representing the state of congestion, which are present inthe response from the interconnected station on the output side, and theelimination of the congestion state also can be detected from theaverage response time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematically the configuration of the station of thepreferred embodiment of the present invention is in FIGS; this figureshows a state in which congestion has occurred in a specific session;

FIG. 2 illustrates schematically the configuration of the station of thepreferred embodiment of the present invention is in FIGS; this figureshows a state in which congestion has occurred in a specific SMSC;

FIG. 3 illustrates schematically the configuration of the station of thepreferred embodiment of the present invention is in FIGS; this figureshows a state in which congestion has occurred in all the SMSC;

FIG. 4 illustrates congestion control executed in the PPG which is astation in accordance with the present invention; and

FIG. 5 illustrates an example of prior art configuration of theallocation system of multimedia messages.

BEST MODE FOR CARRYING OUT THE INVENTION

The configuration of the station of the preferred embodiment of thepresent invention is shown schematically in FIGS. 1 to 3. FIG. 1 shows astate in which congestion has occurred in a specific session. FIG. 2shows a state in which congestion has occurred in a specific SMSC. FIG.3 shows a state in which congestion has occurred in all the SMSC.

FIG. 1 shows only the configuration of the MMS 1, PPG 2, and SMSC 3 inthe multimedia message allocation system shown in FIG. 5. The PPG 2 iscomposed of 2 units: a first PPG (PPG1) 21 and a second PPG (PPG2), andthe SMSC 3 is also composed of two units: a first SMSC (SMSC1) 31 and asecond SMSC (SMSC2) 32.

The congestion control means of the station in accordance with thepresent invention will be explained hereinbelow with reference toFIG. 1. If the MMS 1 receives a multimedia message (MM-message), theMM-message is stored in a mailbox 1 a of the subscriber, which is acustomer in the mailbox 1 a, a reception notification to the customer isproduced, and transfer thereof is initiated. As a result, the MMS 1sends a push transfer request of notification, for example, to the firstPPG 21. This push transfer request is received by an input interface 21a of the first PPG 21 and temporarily stored in a buffer memory 21 b. Aninternal processing unit 21 c reads successively the push transferrequests that were stacked in the buffer memory 21 b and produces asession establishment request so that a network corresponding to eachpush transfer request is initiated. The session establishment request istemporarily stored in a corresponding memory of buffer memories 21 d, 21e, 21 f, 21 g provided for each of the four provided output interfaces21 h, 21 i, 21 j, 21 k. If we assume that the session establishmentrequest is stored in the buffer memory 21 d, then the sessionestablishment requests that were stacked in the buffer memory 21 d areread successively and sent from the output interface 21 h to the firstSMSC 31.

The sent session establishment requests are received in an interface(I/F) 31 a of the first SMSC 31 and sent as short messages from thefirst SMSC 31 to a portable terminal not shown in FIG. 1 of thedestination address. Further, if the session establishment request isstored in the buffer memory 21 e, then the session establishmentrequests that were stacked in the buffer memory 21 e are readsuccessively and sent from the output interface 21 i to the first SMSC31. The sent session establishment requests are received in an interface(I/F) 31 b of the first SMSC 31 and sent as short messages from thefirst SMSC 31 to a portable terminal not shown in FIG. 1 of thedestination address. Further, if the session establishment request isstored in the buffer memory 21 f, then the session establishmentrequests that were stacked in the buffer memory 21 f are readsuccessively and sent from the output interface 21 j to the second SMSC32. The sent session establishment requests are received in an interface(I/F) 32 a of the second SMSC 32 and sent as short messages from thesecond SMSC 32 to a portable terminal not shown in FIG. 1 of thedestination address. Furthermore, if the session establishment requestis stored in the buffer memory 21 g, then the session establishmentrequests that were stacked in the buffer memory 21 g are readsuccessively and sent from the output interface 21 k to the second SMSC32. The sent session establishment requests are received in an interface(I/F) 32 b of the second SMSC 32 and sent as short messages from thesecond SMSC 32 to a portable terminal not shown in FIG. 1 of thedestination address.

Similar operations are also carried out with respect to sessionestablishment requests sent from the second PPG 22 to the first SMSC 31and second SMSC 32. Here, if the message number of the sessionestablishment requests sent from the first PPG 21 and second PPG 22exceeds the amount that can be processed in the first SMSC 31 and secondSMSC 32, then congestion occurs in the first SMSC 31 and second SMSC 32.In this case, the definition of congestion occurrence is based on any ofthe below-described events. In this definition the first PPG 21 andsecond PPG 22 are considered as a PPG, and the first SMSC 31 or secondSMSC 32 is considered as the SMSC.

(1) When an error indicating the congestion of the session was returnedfrom the SMSC with respect to a message submit_sm or message data_sm ofthe message transfer request from the PPG to the SMSC.

(2) When the response to message submit_sm or message data_sm of themessage transfer request contains a congestion_state parameterrepresenting the congestion state in percents and the value of thisparameter reaches a value indicating the congestion of the SMSC.

(3) When the average response time from the SMSC to k latest requestsfrom the message transfers request from the PPG exceeds m times of theaverage response time in a normal state. Here, k and m can be set andvaried by parameters or the like.

It is assumed that the occurrence of congestion in the session in theinterface 31 a of the first SMSC 31, which is an interconnected stationof the first PPG 21, is detected based on this definition. This is shownby the buffer memory 21 d becoming a Full Queque as {circle around (1)}in FIG. 1. When congestion of the interconnected station thus occurs ina specific SMPP session, the first PPG 21 eliminates the congestion inthe manner as follows. Thus, the first PPG 21 continues the service byswitching the messages to the interface 31 b, which is another SMPPsession directed toward the first SMSC 31, as shown by {circle around(2)} in the figure, so that the number of messages directed toward thissession in a unit interval becomes 1/m or less.

Thus, in the PPG which is the station in accordance with the presentinvention, when congestion occurs in the PPG interconnected station in aspecific SMPP session, the PPG continues the service by switching themessages to another SMPP session directed toward the same SMSC so thatthe number of messages directed toward this session in a unit intervalbecomes 1/m or less.

If the acceptance response to a push transfer request from the MMS 1 tothe PPG is delayed for the prescribed time when congestion has occurredin the PPG interconnected station in a specific SMPP session, then, theacceptance number of push transfer requests can be reduced. Therefore,the congestion occurring in a specific SMPP session can be graduallyeliminated. This delay time can be considered as the below-describeddelay time Dt.

Further, let us assume that congestion was detected to occur in both thesession in the interface 31 a and the session in the interface 31 b ofthe first SMSC 31 which is an interconnected station of the first PPG21. This is shown by the buffer memory 21 d and buffer memory 21 ebecoming a Full Queue as {circle around (1)}{circle around (3)} in FIG.2. When congestion of the interconnected station thus occurs in all theSMPP sessions directed toward the first SMSC 31, the first PPG 21eliminates the congestion in the manner as follows. Thus, when all thesessions directed toward the first SMSC 31 are in a state of PPGinterconnected station congestion or closed state, the first PPG 21continues the service by distributing the messages equally to the secondSMSC 32 which is not in a congested state, as shown by {circle around(4)} in FIG. 2.

Thus, when the PPG interconnected station congestion has occurred or aclosed state has been assumed in all the sessions directed toward aspecific SMSC in the PPG, which is the station in accordance with thepresent invention, the PPG continues the service by distributing themessages equally to other SMSC.

If the acceptance response to a push transfer request from the MMS 1 tothe PPG is delayed for the prescribed time when the PPG interconnectedstation congestion has occurred or a closed state has been assumed inall the sessions directed toward a specific SMSC in the PPG, then, theacceptance number of push transfer requests can be reduced. Therefore,the congestion that has occurred in all the sessions of a specific SMSCcan be successively eliminated. This delay time can be considered as thebelow-described delay time Dt.

Further, let us assume that congestion was detected to occur in all thesessions of the first SMSC 31 and second SMSC 32 which are theinterconnected stations of the first PPG 21. This is shown by all thebuffer memories from the buffer memory 21 d to the buffer memory 21 gbecoming a Full Queque as {circle around (1)}{circle around (3)}{circlearound (5)} in FIG. 3. When congestion of the interconnected stationsthus occurs in all the SMPP sessions directed toward the first SMSC 31and second SMSC 32, the first PPG 21 eliminates the congestion in themanner as follows. Thus, when the PPG interconnected station congestionhas occurred or a circuit block state has been assumed in the first SMSC31 and second SMSC 32, the first PPG 21 denies the acceptance of thepush transfer request from the MMS 1. As a result, the filling amount ofbuffer memories from the buffer memory 21 d to buffer memory 21 gdecreases gradually and the of PPG interconnected station congestion orcircuit block state is eliminated.

Thus, in the PPG, which is the station in accordance with the presentinvention, when the PPG interconnected station congestion has occurredor a closed state has been assumed in all the SMSC, the PPG denies theacceptance of the push transfer request from the MMS, therebyeliminating the PPG interconnected station congestion or circuit blockstate. Further, instead of denying the acceptance of the push transferrequest, the acceptance response to the push transfer request from theMMS 1 to the PPG may be delayed for the prescribed time. This delay timecan be considered as the below-described delay time Dt. As a result, theacceptance number of push transfer requests can be reduced. Therefore,the PPG interconnected station congestion or circuit block state in allthe SMSC can be gradually eliminated.

As described hereinabove, in the station in accordance with the presentinvention, when congestion occurs in an interconnected station on theoutput side, the service can be continued by allocating messages toanother session on the output side or to another interconnected stationon the output side. In addition, the congestion may be eliminated byreturning the response to the request from the interconnected station onthe input side with a prescribed delay. Thus, in the station inaccordance with the present invention, a mechanism is provided fordetecting changes in the transfer efficiency on the output side and theacceptance number on the input side is reduced when the transferefficiency has degraded. Further, when congestion occurs in all theinterconnected stations on the output side, the acceptance of therequest from the interconnected station on the input side may be denied.Thus, with the station in accordance with the present invention, theoccurrence of congestion can be prevented or congestion can beeliminated without additional improvements of the interconnectedstations. Therefore, the congestion control of the SMSC that heretoforerequired the maintenance personnel to conduct monitoring and take careof the system can be automated, thereby making contribution to thereduction of maintenance and operation cost of the PPG.

As described hereinabove, because the PPG conducts congestion control,the congestion that has occurred in the SMSC can be graduallyeliminated. Here, the definition of “PPG interconnected stationcongestion” elimination is based on the occurrence of any of thefollowing events.

(1) The PPG issues a message enquire_link request, which is a circuitstate verification message, with n-second intervals to the SMPP sessionthat assumed a PPG interconnected station congestion state. Thecongestion is considered to be eliminated when the average response timeto the k latest message enquire_link requests is within the averageresponse time in a normal state. The k and transmission interval spacingn can be set and varied by parameters or the like.

(2) The congestion is considered to be eliminated when the averageresponse time to the latest k message enquire_link requests is below theaverage response time in a normal state.

Once congestion has been detected to be eliminated in the session inwhich the congestion has occurred in the PPG based on such definition,the above-described congestion control relating to this session iscancelled.

However, congestion occurs not only in the interconnected stations, butalso in the PPG which is a station by itself. Explanation will beconducted below by considering the first PPG 21 as an example, withreference to a graph illustrating a filling ratio shown in the upperpart in FIG. 4. In the first PPG 21 shown in FIGS. 1 to 3, the acceptedunprocessed messages or requests are accumulated in the buffer memory 21b. Assuming that the maximum capacity available for accumulation in thebuffer memory 21 b is 100%, if the filling ratio exceeds h %, then the“PPG own station congestion” is considered to occur as an excess over anamount that can be processed in the internal processing unit 21 c.Further, the filling ratio becoming less than 1% defines the “PPG ownstation congestion”. Here, h and l can be set and varied by parametersor the like.

If the filling ratio in the buffer memory 21 b in the first PPG 21 isdetected to exceed h %, a decision is made that a “PPG own stationcongestion” has occurred and the first PPG 21 sends areception-acceptance response (push-response) to the push transferrequest from the MMS 1 after the delay time Dt, which can be calculatedby the following formula, elapses.

Dt=SMPP average response time/SMPP session number×S  (1)

Here, S is a margin ratio less than 1, that can be set and varied byparameters or the like. Further, when the in the buffer memory 21 b ofthe becomes 100%, the first PPG 21 denies a push transfer request fromthe MMS 1 until the filling ratio becomes lower than h %. If the PPGconducts congestion control as described above, the congestion thatoccurred in the own station is gradually eliminated. Further, when thefilling ratio becomes less than 1%, the response to the push transferrequest is sent without any delay to the MMS 1.

The above-described congestion control executed in the PPG which is thestation in accordance with the present invention will be explained belowwith reference to FIG. 4.

The SMPP response time in the output interfaces 21 h-21 k of the firstPPG 21 are measured in the first PPG 21. Changes in the measured SMPPresponse time with time t are shown by a graph presented in the lowerpart of FIG. 4. In this graph, time ta represents the average responsetime in the normal state to the session establishment request. When theaverage SMPP response time to k latest session establishment requestsexceeds the time mta obtained by multiplying the time ta by m, thencongestion is assumed to occur in the interconnected station of thefirst PPG 21 and the PAP response time, which is a response time to thepush transfer request in the input interface 21 a, is adjusted. Thisadjustment is conducted by delaying the reception-acceptance responsefor the delay time Dt calculated by Formula (I) presented above.

In the upper part of FIG. 4, there is shown a graph illustrating changesin the filling ratio with time t in the buffer memory 21 b where theaccepted unprocessed messages or requests are accumulated. Variations ofthe filling ratio in the buffer memory 21 b are monitored and when thefilling ratio exceeds h %, a decision is made that congestion hasoccurred in the first PPG 21 and the PAP response time, which is aresponse time to the push transfer request in the input interface 21 a,is adjusted. This adjustment is conducted by delaying the response forthe delay time Dt calculated by Formula (I) presented above. When thefilling ratio becomes less than 1%, a decision is made that thecongestion in the first PPG 21 was eliminated and the adjustment of thePAP response time is canceled.

The explanation above was considered with respect to the PPG as thestation in accordance with the present invention, but the presentinvention is not limited to such a configuration, and the congestioncontrol means provided in the station in accordance with the presentinvention also can be applied to station in which the occurrence ofcongestion cannot be autonomously prevented or eliminated.

INDUSTRIAL APPLICABILITY

As described hereinabove, in the station in accordance with the presentinvention, when congestion occurs in the own station or aninterconnected station on the output side, the throughput on the inputside is reduced by delaying for the prescribed time the response to arequest to receive and accept the message from the interconnectedstation on the input side. As a result, the degree of retention on theoutput side can be gradually reduced and the congestion of the ownstation or the interconnected station on the output side can beeliminated.

Furthermore, when congestion occurs in the interconnected station on theoutput side, message information of the session where the congestion hasoccurred is switched to another session and distributed to otherinterconnected stations on the output side. As a result, the congestionin the interconnected station on the output side can be eliminated evenfaster. The occurrence of congestion in the interconnected station onthe output side can be detected from the average response time orparameters representing the state of congestion, which are present inthe response from the interconnected station on the output side, and theelimination of the congestion state also can be detected from theaverage response time.

1. A station for receiving a message from an interconnected station onthe input side and transmitting message information relating to thereceived message to an interconnected station on the output side,comprising response means for returning a response to a request toreceive and accept a message to the interconnected station on the inputside when receiving said message from said interconnected station; andcongestion detection means for detecting that congestion has occurred inthe interconnected station on the output side, wherein when occurrenceof congestion is detected by said congestion detection means, saidresponse means conducts congestion control by responding with a delayfor a prescribed time to the request to receive and accept said messagefrom the interconnected station on the input side.
 2. The stationaccording to claim 1, wherein said prescribed delay time is a timeobtained by dividing an average response time from the interconnectedstation on the output side by a session number in the interconnectedstation on the output side that is multiplied by a margin ratio.
 3. Thestation according to claim 1, wherein the congestion control is alsoconducted with switching means for switching said message information ofthe session in which the congestion has occurred to another session whenthe occurrence of congestion is detected by said congestion detectionmeans.
 4. The station according to claim 3, wherein when there are aplurality of interconnected stations on the output side and congestionhas occurred or a closed state has been assumed in all the sessions to aspecific interconnected station on the output side, said switching meansdistributes and sends said message information to other interconnectedstations on the output side.
 5. The station according to claim 1,wherein said congestion detection means detects that congestion hasoccurred in the interconnected station on the output side when an errorindicating congestion is returned from the interconnected station on theoutput side in response to a request to transfer said messageinformation to the interconnected station on the output side.
 6. Thestation according to claim 1, wherein said congestion detection meansdetects that congestion has occurred in the interconnected station onthe output side from a parameter representing a congested state in theresponse from the interconnected station on the output side to a requestto transfer said message information to the interconnected station onthe output side, this parameter being contained in said response.
 7. Thestation according to claim 1, wherein said congestion detection meansdetects that congestion has occurred in the interconnected station onthe output side when the average response time in a plurality of thelatest responses has reached m times (where m>1) of the average responsetime in the normal state, in the response from the interconnectedstation on the output side to a request to transfer said messageinformation to the interconnected station on the output side.
 8. Thestation according to claim 1, comprising issuance means for issuing acircuit state verification request with a prescribed period with respectto a session in the interconnected station on the output side that hasis to be in a congested state by said congestion control means, whereinsaid congestion detection means detects that a congested state in saidsession has been eliminated when the average response time in aplurality of the latest responses to the issued requests from saidissuance means has become equal to or less than the average responsetime in the normal state.
 9. A station for receiving a message from aninterconnected station on the input side and transmitting messageinformation relating to the received message to the interconnectedstation on the output side, comprising response means for returning aresponse to a request to receive and accept a message to theinterconnected station on the input side when receiving said messagefrom said interconnected station; and congestion detection means whichdetects the occurrence of congestion in the own station when the fillingratio in a buffer memory that stores said messages or received requeststhat have not been completely processed exceeds a prescribed fillingratio, wherein when the occurrence of congestion in the own station isdetected by said congestion detection means, said response meansconducts congestion control by responding with a delay for a prescribedtime to the request to receive and accept said message from theinterconnected station on the input side.
 10. The station according toclaim 9, wherein said prescribed delay time is a time obtained bydividing an average response time from the interconnected station on theoutput side by a session number in the interconnected station on theoutput side that is multiplied by a margin ratio.
 11. The stationaccording to claim 9, wherein the congestion control is also conductedwith switching means for switching said message information of thesession in which the congestion has occurred to another session when theoccurrence of congestion in the interconnected station on the outputside is detected by said congestion detection means.
 12. The stationaccording to claim 11, wherein when there are a plurality ofinterconnected stations on the output side and congestion has occurredor a closed state has been assumed in all the sessions to a specificinterconnected station on the output side, said switching meansdistributes and sends said message information to other interconnectedstations on the output side.
 13. The station according to claim 9,wherein said congestion detection means detects that congestion hasoccurred in the interconnected station on the output side when an errorindicating congestion has been returned from the interconnected stationon the output side in response to a request to transfer said messageinformation to the interconnected station on the output side.
 14. Thestation according to claim 9, wherein said congestion detection meansdetects that congestion has occurred in the interconnected station onthe output side from a parameter representing a congested state in theresponse from the interconnected station on the output side to a requestto transfer said message information to the interconnected station onthe output side, this parameter being contained in said response. 15.The station according to claim 9, wherein said congestion detectionmeans detects that congestion has occurred in the interconnected stationon the output side when the average response time in a plurality of thelatest responses has reached m times (where m>1) of the average responsetime in the normal state, in the response from the interconnectedstation on the output side to a request to transfer said messageinformation to the interconnected station on the output side.
 16. Thestation according to claim 9, comprising issuance means for issuing acircuit state verification request with a prescribed period with respectto a session in the interconnected station on the output side that isdetected to be in a congested state by said congestion control means,wherein said congestion detection means detects that the congested statein said session has been eliminated when the average response time in aplurality of the latest responses to the issued requests from saidissuance means has become equal to or less than the average responsetime in the normal state.